A wide variety of transparent films are well known in the art as coatings for panel substrates. Sometimes these films are a permanent component of a film stack and other times they are placed removably on a surface of a substrate (e.g., to protect the substrate surface against contamination). Substrate surfaces are often prone to contamination during manufacturing and installation processes. Removable transparent films used to protect a panel substrate against contamination are exemplified in U.S. patent application Ser. Nos. 10/009,291 and 10/009,284, the entire teachings each of which are herein incorporated by reference. Such removable films are often removed by a washing process. Since transparent films are typically invisible to or (at least not easily seen with) the naked eye, it can be difficult to determine whether a removable film is present on a substrate.
It would be desirable for manufacturers of a panel to be able to determine visually whether a transparent film has been placed on the panel substrate. Occasionally, manufacturers may inadvertently omit the removable transparent film during manufacturing. Sometimes, manufacturers are unable to tell if the removable transparent film has been yet applied.
It would also be desirable for the consumer or the person washing the substrate surface (e.g., when it is desired to remove the removable transparent film) to be able to tell whether the removable transparent film has been completely removed from the substrate surface during washing. A substrate surface may serve a functional purpose, for example it may be hydrophilic or photocatalytic. In these cases, the functional characteristics of such functional coatings may not be fully exhibited until the removable transparent film is completely removed.